Effects of displacement from marine renewable developments on seabirds breeding at the Isle of May

Executive Summary

• Offshore renewable developments have the potential to impact on seabirds by displacing individuals from foraging habitats. The impact of displacement is particularly important for breeding seabirds that, as central place foragers, are constrained to obtain food within a certain distance from the breeding colony. The current worst case scenario is that displacement causes 100% mortality, so there is a need to model more realistic consequences of displacement.
• Displacement is likely to result in changes to daily energy and time budgets. Such changes may impact on the body condition of adult breeders which, in turn, can affect breeding success, adult survival and, ultimately, population size. Additionally, breeding success may be affected directly if provisioning rates alter significantly.
• The Forth and Tay Offshore Wind Developers Group ( FTOWDG) have exclusivity licences for proposed wind farm developments in the outer Forth and Tay which are offshore from a suite of SPAs for seabird species that will potentially interact with these developments. As part of the environmental evaluation of these developments there is a need to assess the potential impacts of displacement on breeding birds.
• This report presents a displacement model for adult common guillemots Uria aalge rearing chicks on the Isle of May (part of Forth Islands SPA) in relation to the proposed offshore wind farm at Neart na Gaoithe. The model estimates the consequences of displacement and barrier effects on the time/energy budget of breeding birds.
• Our model incorporates several novel features resulting in a step change in the degree of realism captured in terms of incorporating how guillemots use their foraging landscape and in how their fish prey are distributed within it.
• The model compares the time/energy budget of 1,000 breeding guillemots over a 24 hour period in the absence or presence of a wind farm. The model is based on assumptions regarding behavioural change in response to a wind farm and explores scenarios simulating different prey distributions (dispersed or patchy) and different levels of interference competition among guillemots feeding in the same patch.

Under all scenarios, the presence of the Neart na Gaoithe wind farm resulted in an increase in the average costs of foraging. For example, where prey were randomly distributed, mean flight and foraging costs in the absence of the wind farm were 1.18 h (± 0.60 h) and 2.19 h (± 0.96 h) respectively; equivalent values in the presence of the wind farm were 1.60 (±0.67) and 2.58 (± 1.57) respectively. Under this scenario, the mean number of birds displaced was 101, and the wind farm was a barrier to movement for 44 birds.

• The impact of displacement is driven by two main processes: 1) the increased travelling costs to the subset of the population that is displaced or for which the wind farm forms a barrier to movement, and 2) the reduction in average prey densities in the remaining habitat due to intensified intra-specific competition, affecting not just displaced birds but the population as a whole.
• These results indicate that displacement effects on seabird populations could be important and therefore merit further consideration. The most appropriate method of estimating the population consequences of displacement is to link time-energy budget models of foraging with population models under a range of plausible scenarios of displacement. The report describes a framework for undertaking this linked modelling based on three components:
  • A time-energy budget model in the absence of a wind farm which extends the model presented here to produce a cumulative profitability surface over the course of the breeding season from which consequences on adult survival and breeding success are estimated.
  • A time-energy budget model in the presence of a wind farm in which the consequences of displacement and barrier effects on demographic rates are quantified.
  • A stochastic time-specific matrix model which quantifies the population consequences of displacement in three steps: a) a retrospective analysis of population change in relation to environmental conditions; b) a forecasting analysis of predicted population change under scenarios of future environmental change which provides a baseline for c) the predicted
• In conclusion, our model demonstrates that displacement of foraging seabirds from an offshore wind farm could result in changes to their time/energy budgets with potential consequences for breeding performance and/or survival. It also lays the foundation for estimating population consequences of displacement by linking time-energy budget models of foraging with population models.